Polymers each having a polyalkylene glycol chain are imparted various properties such as hydrophilicity, hydrophobicity, and steric repulsion by adjusting their chain lengths and selecting alkylene oxides forming the polymers. These polymers are used as soft segments in various applications such as adhesives and sealants, flexibility-imparting components, and detergent builders.
In recent years, these polymers have been tentatively used as admixtures for cement which are added to cement compositions such as cement pastes, mortar, and concrete. Such admixtures for cement are generally used as agents such as water-reducing agents that increase the fluidity of cement compositions and reduce the amount of water in the cement compositions so that cured products of the cement compositions are capable of having improved properties such as strength and durability. Conventionally used water-reducing agents are naphthalene-based water-reducing agents; currently, polycarboxylic water-reducing agents having polyalkylene glycol chains are newly proposed as those having high water-reducing ability because the polyalkylene glycol chains serve as dispersing groups for dispersing cement particles owing to their steric repulsion. As a result, such water-reducing agents are widely used as high-performance AE water-reducing agents at the present time.
There is disclosed a copolymer for an admixture for cement that is obtained by copolymerizing an unsaturated carboxylic monomer and an unsaturated polyalkylene glycol ether monomer (for example, see Patent Document 1). In this copolymer for an admixture for cement, a carboxyl group derived from the unsaturated carboxylic monomer serves as an adsorbing group that adsorbs cement particles, while a polyalkylene glycol chain derived from the unsaturated polyalkylene glycol ether monomer serves as a dispersing group that disperses cement particles. The steric repulsion of this polyalkylene glycol chain gives reasonably high dispersibility to an admixture for cement. In order to further reduce the amount of an admixture for cement, however, an admixture for cement with higher dispersibility is demanded.
Incidentally, thiol compounds that are compounds each having one or more mercapto groups (thiol groups, SH groups) is used in various applications utilizing the specific reactivity of the mercapto group. For example, high-molecular-weight thiol compounds that are obtained by introducing mercapto groups into polyether compounds are focused on as those widen the range of the applicable fields of the conventional polyether compounds, such as (poly)alkylene glycol, suitable as soft segments for adhesives and sealants, and components for imparting flexibility to various polymers.
Examples of the thiol compound prepared by introducing a mercapto group into a conventional polyether compound include: a polyether having a mercapto group(s) at either end or both ends obtained by adding a thio carboxylic acid to a polyether having a double bond(s) at either end or both ends and then decomposing a generated thioester group(s) (see Patent Document 2); and a polymer obtained by block- or graft-polymerizing a monoethylenic unsaturated monomer component to a modified polyether compound in which a mercapto group-containing compound is introduced into a polyether compound by esterification reaction as a biodegradable water-soluble polymer used as a detergent builder (see Patent Document 3). In addition, there is disclosed that a polyalkylene glycol chain-containing polymer obtained by using a thiol compound as a polymeric chain transfer agent based on the property that hydrogen is easily extracted from a mercapto group and a radical is generated to serve as a polymerization-starting point is suitably used as an admixture for cement and the like (see Patent Document 4). Further, Aldrich Corporation markets Poly(ethylene oxide), 4-arm, thiol terminated (product No. 565725, see Non-Patent Document 1), and Pentaerythritol tetrakis(3-mercaptopropionate) Pentaerythritol tetrakis(3-mercaptopropionate) (product No. 381462, see Non-Patent Document 2) as polythiols free from a polyethylene glycol chain.
However, the conventional polyether compounds and thiol compounds produced by introducing mercapto groups thereinto have room for sufficiently higher dispersibility (water-reducing ability) currently desired and for being more useful compounds in more fields. In addition, there is room for easier, more efficient, and less expensive methods for producing compounds having such extremely high cement dispersibility.    Patent Document 1: JP-A 2001-220417    Patent Document 2: JP-B 7-13141    Patent Document 3: JP-A 7-109487    Patent Document 4: JP-A 2007-119736    Non-Patent Document 1: Aldrich advancing Science 2007-2008 Japan, Sigma-Aldrich Japan, page 2032, upper left column    Non-Patent Document 2: “Pentaerythritol tetrakis(3-mercaptopropionate)”, [online], 2007, Sigma-Aldrich Japan, [searched on Sep. 5, 2008], Internet <URL: http://www.sigmaaldrich.com/catalog/search/ProductDetail/AL DRICH/381462>